All fixed fuel tanks, such as those commonly used in boats and wherein the fuel tank is housed in the hull of the boat, commonly include a vent conduit or vent line providing a means for venting the fuel tank to the atmosphere outside of the boat hull. The vent line permits air to be pulled into the tank when the fuel in the tank is consumed and permits air in the tank to be exhausted to the atmosphere when the tank is filled or when there is expansion of the volume of the fluids contained in the fuel tank. In the prior art arrangements such as those where a fuel tank is housed in a boat hull, the vent line provides an open passage between the outside of the boat hull and the fuel tank. As fuel in the tank is consumed, air having a high moisture content is drawn into the fuel tank through the vent line. The moisture may condense in the fuel tank and result in accumulation of water in the fuel tank.